Rhenium (Re) is one of the rarest metals on earth and found almost exclusively in copper sulfide ore deposits containing extractable quantities of molybdenum (Mo). Re is found within the molybdenite fraction of this specific type of copper (Cu) ore. As a result, a number of processes have been developed to isolate Re from this fraction.
U.S. Pat. No. 3,739,549 recovers Re from ore material by using a roasting process. The Mo and Re is first separated from the Cu by a froth floatation process. The Mo and Re containing fraction is then subjected to a roasting process to separate the Mo and Re. The Re is converted to a large extent to rhenium heptoxide (Re2 O7) which is volatile and passes off with the gaseous effluents resulting from roasting. The flue gases are subjected to a wet-scrubbing process, wherein the flue gas containing Re2O7 is captured and condensed in a scrubbing solution. The Re2O7 containing scrubber solution is then processed by known techniques to produce ammonium perrhenate, i.e., NH4ReO4. Ammonium perrhenate is the primary source form for the production of Re metal. A majority of the world's Re supply is produced by extraction methods that isolate Re from Cu/Mo/Re ores. However, the process is limited to recovering Re from these types of ores and is not a practical for recovering Re from other Re-bearing materials. A second but smaller source of Re is recycled Re.
Re has a number of industrial uses. For example, U.S. Pat. No. 5,562,817 discloses the use of a Re-platinum (Pt) alloy as a catalyst for catalytic reforming. Catalytic reforming is a chemical process that converts petroleum refinery napthas with low octane ratings into high-octane liquid products. Re can also be added to high-temperature super alloys that are used to make components, such as jet engine parts (see U.S. Pat. No. 6,936,090). The scarcity and cost of Re has brought about the development of a number of methods that are used to recover Re, in particular from Re-bearing product and materials.
For example, United States Patent Application Publication No. 2003/0119658 relates to a process for the recovery of rhenium from a spent Re-bearing catalyst by heating the catalyst in an oxidizing atmosphere at a temperature effective to sublime a portion of the rhenium as a volatized oxide. The Re and Pt in the catalysts can be recovered. However, the process is limited to recovering these metals from spent catalysts.
The recovery of Re from super alloy waste and residue materials is also commercially interesting. Super alloys generally contain 50 to 80% of nickel, 3 to 15% by weight of at least one or more of the elements cobalt (Co), chromium (Cr), and aluminum (Al) and 1 to 12% by weight of one or more of the elements Re, tantalum (Ta), niobium (Nb), tungsten (W), Mo, hafnium (Hf) and Pt. United States Patent Application Publication No. 2009/0255372 discloses a process for recovering Re and other valuable metals from a super alloy containing waste or residue material by digesting the super alloy material in a salt melt. The salt melt contains 60-95% by weight of NaOH and 5-40% by weight of Na2SO4. The Re and other metals can then be recovered with the use of known techniques such as selective precipitations and ion exchange techniques. For example, Re is recovered by passing the digested material containing Re over an ion exchange column (see also U.S. Pat. No. 6,936,090). However, the process does not describe being able to recover Re from a variety of materials and suggests recovering Re from ion exchange columns.
Thus, a need exists for a method that can recover Re from a variety of Re-bearing materials at a low cost.
The present invention provides for an economical method of extracting Re and other valuable metals from Re-bearing materials, including nontraditional forms of industrial Re-bearing materials, which were previously overlooked as a source from which to extract Re because no economical extraction process existed. For example, a number of Re-bearing materials have been disposed of in landfills due to the lack of a process that could efficiently recover Re. In some instances, this Re-bearing material was treated in nickel/cobalt recycling processes but only for the recovery of nickel and cobalt constituents and not for the Re content. Once subjected to those nickel/cobalt recycling processes, the Re was alloyed or otherwise diluted to the extent where the possibility of efficiently recovering Re with previously known methods was remote if not impossible.